1. Field of the Invention
The present invention relates to a method for forming a field oxide layer in a high integrated semiconductor device, and more particularly to a method capable of minimizing a bird's beak.
2. Description of the Prior Art
A number of isolation techniques of a semiconductor device have been developed in order to improve the characteristics of a device corresponding to integration degree.
In general, a diversity of field oxide layers are made by using a LOGOS (Local Oxidation of Silicon) and PBL(Polysilicon Buffered LOGOS) process, which is a modification of the LOGOS process.
Namely, a pad oxide layer and a resistant layer of oxidation, such as nitride, layer, are in order deposited on a semiconductor substrate, and a predetermined portion of the resistant layer of oxidation is removed, what we call isolation etching. Finally, an exposed substrate is oxidized in a portion which is the nitride removal region.
In another conventional method for making a field oxide layer, a polysilicon layer, additionally, is used on the above oxide layer in order for a bird's beak not to increase.
Furthermore, for solving the problem of decreasing an active region, which is generated by the bird's beak formed in an edge of the field oxide layer, a spacer layer is formed at the side wall of etched materials after the isolation etching. Also, in order that the field oxide layer has not high topology, the substrate is etched at the time of isolation etching and the oxidation processing can be additionally executed after a trench processing.
However, the conventional methods for forming the field oxide layers form a poor profile of itself and cause a complexity in that a planarization process, such as dry planarization etching or CMP(Chemical mechanical polishing), which deposits a thick oxide layer on the resulting structure, is needed to overcome the topology, which results from the combination of narrow trench and wide trench, which leaves a problem in that it is very difficult to smoothly planarize the thick oxide layer.